Early Studies of Mechanisms of Racemization of Octahedral Metal Complexes

Department of Chemistry, Northwestern University, Evanston, IL 60208, U.S A.

An overview is given of research done in the fifties on the kinetics and mechanism of racemization of [M(AA)₂]²⁺ (M=Ni, Fe; (AA)=-2,2'-bipyridine, 1,10-phenanthroline). The nickel(II) complexes racemize by a ligand dissociation mechanism, but the iron(II) complexes racemize both by a dissociation and an intramolecular pathway. The intramolecular mechanism for [Fe(phen)₂]²⁺ is believed to take place without Fe-N bond rupture, perhaps by a twist process of the t) pe first proposed' by the late Professor P. Ray, a studeut of P. C. Ray. The rates of acid dissociation of the 1, 10-phenanthroline complexes is independent of acid concentration but that of the 2 2'-bipyridine complexes increase in rate with Increasing acid concentration. At some high acid concentration the rate becomes constant, and this Is believed to be a measure of the rate or M-N bond cleavage.